Intelligent manipulation (e.g., grasping/gripping) of micro- and nanometer-sized objects requires the use of miniaturized microgrippers with integrated force sensors. Currently, micro- and nanomanipulation typically relies purely on visual feedback either from an optical microscope or an electron microscope. The lack of force feedback at the microNewton and nanoNewton level severely limits intelligent micro- and nanomanipulation.
Besides miniaturization and electrical control, microgrippers must be capable of providing multi-axis force feedback to satisfy the following requirements: (i) to protect the microgripper and detect the contact between the microgripper and the object to be manipulated; and (ii) to provide gripping force feedback during grasping to obtain secured grasping while protecting the object to be grasped.
The vast majority of existing microgrippers lack force feedback due to the difficulty of integrating force sensors with microgrippers. The lack of force feedback does not permit force-controlled manipulation and easily causes breakage of microgrippers and damage to the object to be manipulated.
A recently reported electrothermally driven microgripper design is integrated with a single-axis piezoresistive force sensor that is only capable of measuring gripping forces. (See K. Molhave and O. Hansen, “Electrothermally actuated microgrippers with integrated force-feedback,” J. of Micromechanics and Microengineering, 15(6), pp. 1265-1270, 2005.) However, the gripping force sensing resolution is somewhat poor, on the order of milli-Newton that is orders of magnitude worse than what micro-nanomanipulation requires.
A recent paper reports a design of an electrostatically driven microgripper with a single-axis capacitive force sensor that is only capable of measuring gripping forces. (See F. Beyeler, D. J. Bell, B. J. Nelson, Yu Sun, A. Neild, S. Oberti, and J. Dual, “Design of a micro-gripper and an ultrasonic manipulator for handling micron sized objects,” IEEE/RSJ International Conference on Intelligent Robots and Systems, Beijing, China, October, 2006.) Due to the limitation of electrostatic actuation (low force output, small displacements, and high driving voltage), the microgripper design is only capable of grasping objects of a small range of sizes.
The lack of force sensing capabilities along a second-axis down to nanoNewton in existing designs does not allow for the protection of microgrippers and the detection of contact between the microgripper and object to be manipulated. What is needed is design and microfabrication of microgrippers that are capable of grasping micro and nano objects of a large range of sizes and having two-axis force sensing capabilities.